Abstract:The thickness of intact human red cell membrane is measured by a light-microscope technique in which membrane material with a known surface area is extracted into a long, thin cylindrical strand. The radius of the strand is calculated from its known length and surface area. The minimum radius, obtained at high extraction velocities or large membrane tensions, is 55 angstroms. A collapsed membrane cylinder with a mean-mass radius of 55 angstroms would have a membrane thickness of 78 angstroms